1. Field of the Invention
The present invention relates to a cryogenic refrigeration apparatus and a method of controlling a cryogenic refrigeration apparatus.
2. Description of the Related Art
There is known a refrigeration device of cold storage type configured to supply a high-pressure helium gas compressed by a compressor to a refrigerator and return a low-pressure helium gas expanded in the refrigerator to have a reduced pressure back to the compressor, wherein a temperature sensor is provided on the refrigerator side and a bypass passage having a flow rate control valve controlled by a signal from the temperature sensor is provided so that the temperature of the refrigerator is controlled by controlling a pressure difference between the high-pressure side and the low-pressure side of the working gas.
In the refrigeration device described above, one refrigerator is provided for one compressor. In some devices available recently, a plurality of refrigerators are provided for one compressor in order to save energy and reduce cost. For example, the plurality of refrigerators are mounted at a plurality of locations in a given large-sized device or mounted in a plurality of devices of similar type, respectively. In such extremely low temperature refrigeration devices, the common compressor is used to simultaneously operate the plurality of refrigerators, which may be referred to as multi-operation.